The Swiss company Omega has had responsibility for the timing and scoring of Olympic events since 1932. Before the 1976 Games they contacted the International Olympic Committee with a question about the scoreboards they were constructing for the gymnastics. Would it be better, they asked, to replace the traditional boards, which had room for three digits such as, say, 9.50, or 9.85, with one that could display four digits, such as 10.00?

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“I was told, ‘a 10.00 is not possible,’” recalls Daniel Baumat, now the director of Swiss Timing, which like Omega is part of the Swatch Group. “So we only did three digits.”

On Sunday 18 July, the second day of the Montreal Games, a 14-year-old gymnast called Nadia Comaneci made her first appearance. Her routine on the uneven bars that day was flawless, and the judges agreed. One of them approached Baumat, who was working in the arena. “She asked what to do. I said that they could either put up 1.00 or .100 but that there was no possibility for a 10.00. Just as the federation had told me.”

Comaneci received a perfect 1.00.

It is easy to see why the IOC considered 10.00, a score never previously achieved in Olympic competition, to be unachievable. By the time she left Montreal the tiny Romanian had done it seven times. In 1972 the performances of the young Russian Olga Korbut had thrust gymnastics out of the Olympic shadows; in 1976 Comaneci stepped into that spotlight and created a legend.

Korbut must take some of the credit not just for the attention Comaneci received, but for the quality of her performances. Korbut and her Belorussian coach, Renald Knysh, had struck up a fearsome rivalry not just with Comaneci and her coach, Bela Karolyi, but also with the Russian Ludmila Tourischeva and her coach, Vladislav Rastorotsky. The result was a period of huge technical improvement and innovation, which reached its pinnacle in Comaneci’s performances in Canada.

Four times she produced perfect routines in the asymmetic or uneven bars, and three times on the beam. She won three gold medals, for the bars, the beam and the all-around competition, as well as a team silver and a bronze for her floor exercise. The only possible criticism was that she didn’t seem to enjoy it very much. “She seemed,” the Guardian wrote a few years later, “almost inhuman in her exactness.”

There were many possible reasons for that. Comaneci had been born in 1961 in Onesti, a town in the Carpathian mountains, to a car mechanic called Gheorghe and his factory-worker wife, Stefania-Alexandrina. Her talent was spotted at the age of six, when she joined the boarding school for young gymnasts run by Karolyi and his wife, Marta.

Karolyi was a former junior boxing champion, and a member of the national hammer-throwing team. He was to become one of gymnastics’ most successful coaches, both in Romania and again following his defection to the US in 1981, where he coached the 1984 Olympic champion Mary Lou Retton (whose perfect 10 on the vault remains one of America’s golden Olympic memories), the 1991 world champion Kim Zmeskal and the victorious 1996 Olympic team. But some of the methods apparently used by the Karolyis have caused controversy.

In 2008 Emelia Eberle, who joined the school in 1976 aged 12 and now lives in the United States under the name Trudi Kollar, said: “It was brutal. Nobody’s perfect, so obviously we did mistakes. And we, you know, just got smacked everywhere from Bela – on all our body parts. He has huge hands and it hurts.” In 2002 another Romanian gymnast, Rodica Dunca, told ProSport magazine: “On certain days we were hit until blood was pouring out of our nose. You can say it was a concentration camp, or even a prison.” Another gymnast, Ecaterina Szabo, said that after the Karolyis defected “I was so happy that I’d escaped them. I’ll never forget the slaps in the face and the beatings I got from Bela Karolyi.” Geza Pozsar, the Romanian team choreographer who defected with Karolyi, has admitted that he “saw the beating and the abuse”. There is a useful blogpost about the scandal here.

Asked in 2008 to comment on the allegations, Karolyi said: “I ignore it. I’m not even commenting. These people are really trash.” As for Comaneci, at one point while under his care she was rushed to hospital, apparently after drinking bleach. “I didn’t try to die,” she later insisted, “I drank shampoo by mistake.” She admits, though, that the regime was extremely demanding. “Life is tough for everybody,” she said in 2004. “It would be great if you could discover a way of working very little and being successful, but there isn’t one.”

Comaneci’s ability was quickly apparent. Her first international competition as an “adult” came in April 1975, when she became the youngest ever competitor in the International Champions All Tournament at Wembley. “At 13 years old Nadia Comaneci is still both physically too exuberant and spiritually too intense to be the perfect gymnast,” wrote David Hunn in the Guardian, “but give her another year or two and there may be no confining the exquisite talent of this tiny Romanian girl.”

It did not even take that long. The following month she won four out of a possible five gold medals at the European Championships in Skien, Norway, and took a silver in the fifth. And then came Montreal.

Though she did not retire until 1984, Comaneci could never return to the heights she reached as a 14-year-old. When she came back to Wembley in 1977 the Guardian reported that she “looked as if her gymnastics had become a perfunctory chore rather than an expression of zestful grace”.

In Montreal she was 4ft 11in tall and weighed 6st 2lb; by the time she arrived at the world championships in Strasbourg two years later she was seven inches taller and a stone and a half heavier. She won a gold on the beam and a silver in the vault, but admitted that she was “a bit saturated” with gymnastics and said she planned to retire in 1980.

She had lost 10lb by the time of her appearance at the World Cup in Tokyo in 1979 – Romanian officials said it had only been “puppy fat”, but journalists described her as looking “frighteningly emaciated”. She got a perfect score in the floor exercise and changed her mind about retirement.

By the time of the Moscow Olympics, her first appearance in Russia, the little girl who caught the world’s imagination four years earlier had become a young woman. The Guardian’s Frank Keating wrote that “she has filled and lengthened, no longer a kittenish little cog whirling about, but a darkly sombre, concentrating Carpathian 18-year-old who wears a bra and has to shave her armpits”, prompting a bumper postbag from readers who wondered what her lingerie and personal hygiene had to do with anything.

Judges’ scoring brought her glory in 1976, but it was to bring infamy in 1980. She took to the beam, the final event of the combined exercises competition, needing 9.95 to retain her title. Her routine was not perfect, and neither was her landing, but the six judges immediately launched into a heated argument, which lasted nearly half an hour and ended only when Ellen Berger, the East German president of the International Gymnastics Technical Committee, decided that she should get 9.85. This left her tied for second – with an East German – while gold went to a Russian, Alena Davydova.

Then in the individual exercises, the mark displayed for her floor routine – 9.00 – was mysteriously upgraded to 9.50. Berger explained that Britain’s judge, Helen Thomas, had pressed the wrong button, registering 9.50 when she had intended 10, and the score had simply been recalculated in line with her original intentions. A British official denied the button-pressing story and said that the recalculation followed a Romanian team protest. She won gold in the beam, but only after a 10-minute delay in marking her Russian rival, involving exactly the same group of officials who had been involved in the first controversy. When the local favourite’s mark of 9.85 came up, the crowd booed lustily.

She won two gold and two silver medals, but wouldn’t compete in Russia again. When the world championships were held there the following year Comaneci was fully fit, had just won five golds at the University Games in Bucharest and travelled with the Romanian team, but she refused to compete.

Though she was certainly a celebrity, used by the Romanian government both for propaganda and to raise funds – it was on a fundraising tour of America, which brought in $250,000 for the state (but just $1,000 for the star), that Karolyi defected – the style of Comaneci’s life in Romania under Nicolae Ceausescu’s brutal regime is disputed. Newsweek once alleged that she had “lived like a rock star”, detailing her palatial house and extensive staff, but Comaneci said: “I had to live like everybody else. I had to stand in lines, and miss out, and be followed by the police. I had no money, no special treatment. It was all rumours.” Her mother has said that Nadia was raped by the dictator’s son, Nicu, when she was 17 and still a virgin, though Nadia herself has denied this. “My life drastically changed after the Karolyi defection,” she said. “I started to feel like a prisoner. In reality, I’d always been one.”

In 1989, just weeks before the fall of the Ceausescus, she walked for six hours through pitch black, muddy woodland to escape across the border to Hungary, and thence to Austria and finally, upon the aptly named Pan-Am jet Liberty Bell, to the United States. In fact true liberty was delayed until she broke from the apparently abusive clutches of the man who masterminded her escape, a self-employed roofer called Constantin Panait, the following year. Now 50, she lives in Oklahoma with her husband, Bart Conner, who won two gymnastics golds for the US in the 1984 Games. Together they run a gymnastics academy, alongside several other businesses.

It is no longer (officially) possible to compete in the Olympics at 14, or, following changes to the scoring system in 2008, to score a perfect 10. There are very few Olympians who can say with absolute certainty that their achievements will never be equalled, but Nadia Comaneci is one.

What the Guardian said: 20 July 1976

The distinction which Romania’s Nadia Comaneci has received in the team gymnastics championship here is to be applauded by the other participants. Only the great gymnasts have received this accolade in a sport where the competitors are more discriminating than the most pedantic of judges.

But when the 14-year-old European champion received a maximum 10 points for her performance on the asymmetric bars the watching competitors joined the 18,000 crowd in the applause.

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It is believed to be the first time a perfect score has ever been achieved for any apparatus at the Games. Miss Comaneci’s precision on the beam and floor exercises is exact. She moves with measured care although this is obscured by the ease which is such a feature of her performance. On one handstand she swung her legs overhead so tantalisingly slowly that it seemed as if she did not have the momentum to reach the position. But she did – and then lingered there, as if to emphasise the smoothness of the action before continuing her routine.

In addition, Miss Comaneci has the temperament which makes her such a rational favourite for Wednesday’s combined exercises final. Unlike Russia’s Olga Korbut, the charm in her routine is not obvious, she does not appear to be trying to allure the judges or spectators and this restraint is all the more effective because of it.

Larissa Latynina, the Russian coach and former Olympic champion, complained that the maximum score was not deserved because Miss Comaneci should not have taken two steps on dismounting from the bars but only one, which is neater. Although there is some validity in her remark, it was probably motivated by a wish to restore confidence in the girls she is advising. Neither Ludmila Tourischeva, the 1972 Olympic champion, Olga Korbut, nor Russia’s current No1, Nellie Kim, seem likely to disturb Miss Comaneci’s dominance in this form.

However, although Miss Comaneci leads the qualifying competition after the compulsory exercises, Russia’s quantity of talented competitors means that they are still ahead in the team event.

What she said

“Everybody was surprised to see a 14-year-old being able to do the level of gymnastics that I did, but even I didn’t know that I was extraordinary at the time.”